A multiple illumination beam, multiparameter flow cytometer/cell sorter system will be used to study changes in cellular characteristics which occur during normal and abnormal growth and during differentiation in a variety of cell systems. Cells will be characterized by size, as determined by extinction measurements, by forward and orthogonal light scattering behavior at several wavelengths, and by the fluorescence of multiple probes within cells and/or bound to cell surfaces. Flurescent probe-based measurements of DNA and RNA content, of the presence and amount of surface antigens and receptors, and of physiologic characteristics such as membrane permeability, membrane potential, and intracellular pH will be used to identify cells in mized populations and also to characterize these cells as to state of proliferation and maturation. We have developed this analytical approach in extensive studies of lectin- and antigen- stimulated lymphocytes using apparatus similar to that which we propose to acquire; we will continue our efforts at dissecting the sequence of lymphocyte activation and also apply the same techniques to the study of cultured cell lines derived from human teratocarcinomas, bone marrow, vascular and connective tissue, murine and human leukemias, murine smooth muscle cells, promegakaryoblasts, and hepatocytes. Multiparameter analysis these mixed cell populations will be used to derive criteria for sorting subpopulations for biochemical analysis and/or for further study in vitro. The sensitivity of the flow cytometer will also permit analyses of objects smaller than nucleated cells, such as platelets and liposomes.